GATE ECE 2014 Set 1 | Question: 42

Question

The digital logic shown in the figure satisfies the given state diagram when $Q1$ is connected to input $A$ of the XOR gate.

Suppose the XOR gate is replaced by an XNOR gate. Which one of the following options preserves the state

diagram?

• A. Input $A$ is connected to $\overline{Q2}$
• B. Input $A$ is connected to $Q2$
• C. Input $A$ is connected to $\overline{Q1}$ and $S$ is complemented
• D. Input $A$ is connected to $\overline{Q1}$

Answer 1

Here the gate equation is given as $A\oplus S=Q_{1}\oplus S$

Now XOR gate changes to XNOR gate and still the equation remain same, i.e. $A\odot S=Q_{1}\odot S$

Now both equation will be equal when $Q_{1}\oplus S=Q_{1}\odot S’=Q_{1}’\odot S$

So, in place of $Q_{1}$ if we place $Q_{1}’$ both will give similar output.